In cigarette making machines, a cut tobacco braid is continuously produced and subsequently wrapped in a paper tape, to form the so-called continuous rod from which the single cigarettes are cut.
Before being wrapped in the paper tape, the braid is adjusted in shape and size by means of an operation called trimming, during which tobacco threads exceeding a given braid section profile are cut away.
For this operation, trimmers are already known in which two knife disks, mounted coplanar and substantially tangent between each other, of equal diameter and counterrotating, cooperate with a rotating brush, which is driven around a shaft, which is inclined with respect to the tobacco braid feed axis, so that the tobacco braid advances on the trimming knife disks, substantially in the area of their line of tangency, while the brush passes close to the coplanar faces of said disks, in their point of tangency or where the disks are nearest to each other, and cuts the exceeding tobacco threads.
As an alternative to the rotating brush, a trimming element can be used which consistes of a wheel with straight radial paddles, that is, oriented parallelly to the wheel axis.
However, it has been found convenient not to proceed with the uniform braid trimming, but to leave a greater quantity of tobacco at those points of the braid, which wrapped in a continuous rod, will subsequently be cut into single cigarettes.
With this arrangement, the cut tobacco is denser at the ends of the single cigarettes, and this is obviously desired both because cut tobacco leakage from the ends is avoided and for a more uniform and nice looking outer appearance of the cigarettes.
In practice, when it is desired to trim the braid in such a way it presents uniformly interspaced denser areas, the disks present peripherally formed shaped areas, deeper than the plane of the respective disk. The rotation of the two disks is so timed that said deeper peripheral areas meet together periodically and consequently trimming in these areas leaves the braid denser.
If the rotary trimming element is a bristle brush, it is so arranged that the tips of the bristles inflect themselves on the disks at said deeper areas, where the projection is greater, while the bristles will just graze the other parts of the disks. When the trimming element is an oblique wheel with radial paddles, a certain number of consecutive paddles will have to be made lower than the others.
In addition, when the paddle wheel diameter, the pitch of the paddles, and their width have been established, the paddle wheel speed will have to be such that, when a paddle ceases its cutting action on the tobacco braid, the resumption of this action by the next paddle occurs at the cutting line defined by the outgoing paddle or, even better, slightly upstream of this line with a so-called overlapping effect.
With the above devices, an indifferentiated cigarette dense ending is obtained; in other words, this means that the greater cut tobacco density is substantially the same both at the tobacco end of the cigarette and at the end to be connected to the filter plug.
This invention aims to obtain a differentiated density of cigarette ends in such a way that the degree of density at the cigarette ends although being greater than the averge density of the cigarette body, is smaller at the cigarette end intended to be connected to the filter, and greater at the other end. This invention proposes an improved device for trimming the tobacco braid, in cigarette makers, comprising a pair of rotating disks mounted substantially coplanar and substantially tangent between each other, as well as of equal diameter and counterrotating in the direction of the feed axis of the tobacco braid which runs above them, while a trimming element shaped like a paddle wheel, oblique in relation to said feed axis, rotates grazing the disks from the bottom, synchronized and timed with said disks, the device consisting of disks equal to each other, where each disk has an even number of peripheral notches, angularly equidistant between each other, the notches of each disk being alternately formed with different depths while the paddle wheel has two opposite sectors comprising each a number of paddles having heights respectively commensurated with the alternate depths of said notches of the trimming disks so that, by opportunely timing the motions of the paddle wheel and of the disks, different trimming depths will be obtained, which produce a differentiated end density of the single cigarettes, said paddles being set inclined in relation to the axis of rotation of the paddle wheel so as to maintain the necessary overlapping effect in the trimming.
These and other features of the invention and the resulting advantages will be understood from the following detailed description of a preferred embodiment, given as a non restrictive example with reference to the attached drawings.